Apparatus for starting extrusion of filaments from metallic melts

ABSTRACT

An apparatus for extruding molten metals to form continuous filaments is provided with a mechanism for controlling the pressure level across the extrusion orifice which includes a means for introducing a pressurizing gas into the discharge cavity immediately below the orifice and a slide valve positioned downstream from the discharge cavity in the cooling column.

United States Patent 11 1 Junker Dec. 17, 1974 APPARATUS FOR STARTINGEXTRUSION 2,976,590 3/1961 Pond 164/283 5 x ()F FILAMENTS FROM METALLICMELTS 3,216,076 11/1965 Alber et al 164/82 X [75] Inventor: Bernhard T.Junker, Raleigh, NC. [73] Assignee: Monsanto Company, St. Louis, Mo.Prlmary L'mmmer R' Spencer Annear [22] Filed: Dec. 28, 1973 [21] Appl.No.: 429,331 [57] ABSTRACT An apparatus for extruding molten metals toform [52] 164/274 164/82 264/176 F continuous filaments is provided witha mechanism for [51] lift. Cl. B22d 11/08 Controlling the pressure levelacross the extrusion [58] held of Search 164/66 283 fice which includesa means for introducing a pressur- 164/274; 264/176 F izing gas into thedischarge cavity immediately below the orifice and a slide valvepositioned downstream [56] References and from the discharge cavity inthe cooling column.

UNITED STATES PATENTS 2,907.082 10/1959 Pond 164/66 1 Claim, 1 DrawingFigure I2 4 I II IO\ 1 I3 1' I I5 l l9 J -14 2O-HL 21 5 APPARATUS FORSTARTING EXTRUSION OF FILAMENTS FROM METALLIC MELTS This inventionrelates to a melt extrusion apparatus and more particularly to animproved apparatus for extruding low viscosity melts of the variousmetals and metal alloys to form continuous filamentary products.

Methods for forming metallic fibers and filaments by extruding acontinuous stream of molten metal through a small orifice are known andhave been described in US. Pat. Nos. 3,216,076 and 3,658,979. Accordingto these methods, the melt of a metal or metal alloy is extruded at anappropriate velocity into a selective atmosphere. When the hot jetissuing from the extrusion orifice contacts this atmosphere a reactionoccurs which results in the formation of a film about the jet surface.This film stabilizes the filamentary jet or stream against surfacetension break-up until it is solidified by passage through a coolingcolumn.

The apparatus employed in the practice of these methods is comprisedessentially of a crucible for containing the melt with an orificeelement in its base. The crucible is further provided with heating meansto melt the charge and maintain it in the molten condition. In addition,means are provided for applying a positive head pressure to the moltencharge contained within the crucible to force it through the orifice atan appropriate ejection velocity and into a discharge cavity wherecontact is made with the film forming atmosphere.

A troublesome problem commonly encountered when extruding metalfilaments in accordance with these methods is the tendancy for moltenmetal charge to accumulate in the orifice capillary during the course ofthe pressurization cycle for imparting the necessary head pressure overthe melt to effect proper streaming through the orifice. This causesgreat difficulty in attaining a proper streaming after the systembecomes sufficiently pressurized and the production run often has to beaborted.

This problem has now been overcome by controlling the pressure acrossthe orifice while the system is being adjusted to the desired operatingconditions. This is accomplished by introducing a pressurizing gas intothe discharge cavity immediately below the orifice. A slide valvepositioned in the cooling column downstream from the discharge cavityprevents loss of pressure below the orifice when in closed position.

The afore-described procedure may be carried out in an apparatus havinga design as illustrated in the accompanying drawing wherein the singleFIGURE is a schematic sectional view of the presently preferredembodiment of the invention.

There is shown as generally represented by the numeral 10, a typicalassembly for extruding a freestreaming molten jet from a metal melt. Theassembly includes a crucible 11 for containing the melt enclosed withina pressure vessel 12. The crucible is provided with an orifice 13through which is extruded a continuous stream or jet of molten metalgenerally denoted 14. The crucible rests upon a supporting insulatingpedestal 15 of pyrolytic graphite construction which in turn rests uponpedestal l6 and 17 supported by the assembly base plate 18. Withinpedestals l5 and 16 and immediately below orifice 13 is a dischargecavity 19. P0- sitioned beneath discharge cavity 19 is a verticallydisposed elongated cooling column 20. A slide valve 21 is positioned incooling column 20.

When proceeding to pressurize the system to impart the desired extrusionhead pressure over the melt, a pressurized gas (source not shown) isintroduced into discharge cavity 19 through port 22 in flange member 23while slide valve 21 is in closed position to permit pressure control inthe discharge cavity. When the desired operating conditions are attainedfor proper streaming of the melt, slide valve 21 is opened with aresulting rapid depressurization of discharge cavity 19 so that a fullydeveloped molten metal stream through orifice 13 is establishedinstantly. In the open position the slide valve plate is retractedcompletely and does not interfere with streaming in the cooling column.

As indicated, the pressure control is generally at a level which willprevent filling of the orifice capillary with molten metal; however, insome instances it may be desirable to control the pressure to a levelwhich permits back bubbling of discharge cavity gas through the orifice.The latter control may be employed in those instances where gas refiningof the metal charge may be desirable before commencing the extrusionoperation.

It is to be understood that the embodiment disclosed herein is merelyillustrative and that it can be modified or amended and that numerousother embodiments can be contemplated without departing from the spiritand scope of the invention.

1 claim:

1. In an apparatus for forming continuous filaments directly from themelt of a metal, wherein under a positive head pressure the melt isejected through an orifice and into a discharge cavity as a molten metalstream from whence the stream descends in a downward vertical paththrough a cooling column positioned immediately beneath said dischargecavity, the improvement which comprises means for controlling thepressure level across the orifice, said means comprising: a slide valvepositioned in said cooling column downstream from said discharge cavityand means for introducing a pressurizing gas into said discharge cavity.

1. In an apparatus for forming continuous filaments directly from themelt of a metal, wherein under a positive head pressure the melt isejected through an orifice and into a discharge cavity as a molten metalstream from whence the stream descends in a downward vertical paththrough a cooling column positioned immediately beneath said dischargecavity, the improvement which comprises means for controlling thepressure level across the orifice, said means comprising: a slide valvepositioned in said cooling column downstream from said discharge cavityand means for introducing a pressurizing gas into said discharge cavity.